The invention relates to a base for compact fluorescent lamp, and more particularly to a compact fluorescent lamp base which consists of a plastic cap and a plastic body.
Market expectations require the overall length of the lamp to be shorter and shorter. The overall length is determined by the length of the tube portion of the discharge tube and by the height of the fluorescent lamp base incorporating the ends of the discharge tube. Tube portion means a portion bent in several parts or composed of several parts by glass sealing between the two spatially farthest points of the discharge tube. A construction of compact fluorescent lamps is known wherein the fluorescent lamp base contains only the plastic cap for fixing the discharge tube and the plastic body fixed thereto, to which base a separate lampholder can be connected by a releasable joint. In this case, connections ensuring electrical contact and also mechanical joint are made between the lampholder and the base. For ensuring electrical contact, metal parts, particularly metal pins connecting in a releasable way to the electrical contact parts fixed in the lampholder are embedded in the base. The base and the lampholder are fixed mechanically and kept in position by an also releasable mechanical joint providing for exchangeability.
By meeting the market expectations mentioned, a version of the base and lampholder is known wherein the mechanical joint is provided for by forming a hollow in the base, to which a protruding part of the lampholder is connected. This solution exploits the opportunity that the empty space of the base can be utilized which reduces the overall length of the compact fluorescent lamp. This base construction is called an inverted base.
With respect to the present invention, the electrode inleads of the discharge tubes fixed in the base, the metal pins and the mechanical fixing elements formed in the body part of the base are of importance since the electrode inleads are directly fixed to the metal pins in this construction. During fixing, it should be provided for that the electrode inleads cannot get in galvanic contact with each other while the fixing elements ensuring mechanical joint and protruding into the base are also present.
Solutions are known for this type of compact fluorescent lamp bases which is also described in patent specification No. HU-213598. It is seen in this specification that the metal pins for electrical contact are placed at the four corners of an imaginary quadrangle around the axis of symmetry while the electrode inleads from the ends of the discharge tube are at one side. In this construction, the hazard exists that the electrode inleads get in contact with each other during assembly. This hazard is the greater the more portions the discharge tube consists of, in which case the relative position of the discharge tube ends and the metal pins for electrical contact, the position of which is specified in the standard, becomes particularly unfavorable.
It is known from the practice at the same time, that the cap fixing the discharge tube, of the two-part plastic base constructed for the inverted base and lampholder mentioned above, and the body of the base provided with construction elements for electrical and mechanical connection, are in general not fixed to each other sufficiently. E.g., in the base construction according to patent specification U.S. Pat. No. 5,634,820 and also in other base constructions that have become known by public use, the cap and the body are fixed to each other only along the outside perimeter. The axial force exerted when inserting the compact fluorescent lamp into and mainly when pulling it out from the lampholder appears along the perimeter of the cap and the body, and the resistance to pulling and particularly to torsional load is only sufficient if the matching parts are made with extraordinarily high accuracy. This has the consequence that providing a sufficient strength of bond reliably and continuously in the case of this type of base constructions is problematic. This problem is caused by the spread resulted from the mass production of parts and by the requirement for reducing the quantity of material used.
It is therefore seen to be desirable to construct a compact fluorescent lamp base ensuring that the electrode inleads cannot get in contact with each other during assembly when connecting the electrode inleads of the discharge tube to the metal pins, which results in a reduction of shrinkage.
Also, there is a particular need for a base construction enabling to make two-part plastic compact fluorescent lamp bases with a higher bond strength and with an increased resistance both to pulling, bending and torsional load, also in the case when the wall thickness is less than that of the known bases.
The invention is based on the recognition that in the case of compact fluorescent lamp bases of the type described above, fixing of the electrode inleads can be solved by lengthening the parts for mechanical joint with extensions inside the base and by adding further elements to these parts. We have also recognized that the extensions for fixing the electrode inleads can also be made suitable for making an inside connection surface by using further additional elements. This increases the strength of bond between the two parts of the base.